BACTERIA IN CHEESE-MAKING. 263 



The chemical changes, rendering the casein easily digestible, 

 are generally admitted to be in considerable degree due to the 

 action of chemical ferments already mentioned, but it is also 

 admitted that the flavors must be due to the growth of the 

 microorganisms. The molds, which are so important in the 

 ripening of soft cheeses, play no part in the hard cheeses. In- 

 deed, their growth is wholly prevented by the compact mass of 

 the cheese and by the salting, oiling and rubbing which its 

 surface receives. Inside of the cheese, however, the bacteria 

 grow, although rather slowly, and to their action is attributed 

 the chief part of the flavor production. 



To determine with definiteness the species of bacteria which 

 produce the flavors in hard cheeses, has proved a very difficult 

 task. Some species of milk bacteria certainly do produce 

 cheese flavors when they grow in the milk (Fig. 31), but their 



FIG. 31. 



Q) o^ ^ $/^\^\ 



^. Hm\s\^[ 



Bacteria producing cheese flavors. ( Conn.} 



application to cheese-making has not resulted as yet in much 

 success. It is pretty well recognized that the lactic bacteria 

 must be looked upon as the chief organisms engaged in the 

 ripening. At present bacteriologists are by no means satisfied 

 with their results and have indeed reached different con- 

 clusions. Some insist that the lactic bacteria are the sole 

 agents in the process. Others look upon the peptonizing bac- 

 teria as playing a part, either doing the whole or being the 

 most important living factors in the ripening. Others say that 

 the ripening is a long process in which several species of micro- 

 organisms are probably engaged. No one has been able to 

 determine with certainty that any distinct species of bacterium 



